1. Field of the Invention
The present invention relates to a flash apparatus having a plurality of light emission modes of different light emission control schemes.
2. Description of the Related Art
As is well known, a conventional flash apparatus has emission modes of the following two light emission control schemes.
One of the modes is a light emission mode of an automatic control scheme called a normal (external light) automatic scheme or TTL (through the lens) automatic scheme. In this scheme, light emitted by flashing and reflected by an object to be photographed is received by a sensor, and a signal representing the amount of received light is fed back to the flash apparatus, thereby adjusting the light emission amount of the apparatus and providing a proper exposure value.
The other mode is a light emission mode of a so-called open control scheme such as a guide number scheme or a flashmatic scheme. In this scheme, a light emission amount is determined by calculating a proper light emission amount in advance on the basis of data associated with flash photography, which are set in the camera, such as an aperture value, an object distance, a film speed, and an exposure correction value.
For example, according to the guide number scheme as a typical example of this open control scheme, a required light emission amount of the flash apparatus is determined on the basis of aperture value data FNo from an aperture control means, object distance data d (meters) from a distance measuring means, a preset film speed ISO, and an exposure correction value. That is, if ISO=100 and the exposure correction value is .+-.0 ev, a required guide number GNo is given by: EQU GNo=d(m).times.FNo (1)
Equation (1), however, can be established only when the flash apparatus opposes an object to be photographed. When the flash apparatus is to be used in, e.g., a bounce state in which the light emission axis of the apparatus is inclined, equation (1) is not established. In such a case, the following equation (2) must be used: EQU GNo=d(m).times.FNo.times.k (2)
where k is a constant which satisfies k.ltoreq.1.
Since the constant k is determined by the ratio of direct light to reflected light, this value greatly varies depending on a photographic condition, resulting in photography with incorrect exposure.
In this guide number scheme, when the flash apparatus is to be used while it is detached from the camera (OFF-camera state), neither of equations (1) and (2) are established. The following equation (3) must be used instead: EQU GNo=d'(m).times.FNo (3)
where d' is the distance (meters) between the flash apparatus and an object to be photographed.
In this case, however, the distance d' between the flash apparatus and the object cannot be obtained by using a distance output from the distance measuring means on the camera side, and must be measured with the eyes. For this reason, when the flash apparatus is to be used in an OFF-camera state, proper exposure control cannot be expected. In order to realize correct exposure, the distance d' between the flash apparatus and the object must be measured by a cumbersome measuring operation using a measure or the like.
As described above, in the guide number scheme, when the flash apparatus is to be used in a bounce state or an OFF-camera state, proper exposure control cannot be expected. In order to perform proper exposure control in an OFF-camera state, a cumbersome measuring operation must be performed.
In addition, in the guide number scheme, as disclosed in Published Unexamined Japanese Patent Application No. 62-264032, a required light emission amount is determined by obtaining the object distance data d (meters) on the basis of defocus data from automatic focusing output data. If, however, a front converter (focal length/magnification conversion lens) is mounted on the front end portion of a photographing master lens, the data of the distance from the master lens to the object is deviated from the proper data. On the other hand, the aperture value of the master lens is not changed after the front converter is mounted on the master lens. Therefore, if the front converter is mounted, the guide number GNo is given by: EQU GNo=d"(m).times.FNo (4)
where d" is the distance (meters) between the flash apparatus and the object, which is corrected upon mounting of the front converter.
If a rear converter is mounted on the rear end portion of the photographing lens, the aperture value of the master lens is changed from that of the master lens before the rear converter is mounted, although the data of the distance from the master lens to the object is correct. Therefore, if the rear converter is mounted, the guide number GNo is given by: EQU GNo=d(m).times.FNo' (5)
when FNo' is the aperture value data of the master lens, which is corrected upon mounting of the rear converter.
As described above, in order to calculate a required light emission amount upon mounting of a converter, distance data or aperture value data must be corrected. This requires cumbersome operations.